From Wikipedia on 10/13/12
A series of events to produce a result, especially as contrasted to product.
My Own Writing
There’s a difference between a system and a process. A system is a collection of related elements. A process is the movement of information, matter, or energy through a system.
You can think of a process as equivalent to a function in a computer program. It has inputs, outputs and transformations. Certain things are read and certain things are written. It may call or be called by other processes. For example, in sorting your mail, the box of unsorted mail is read and the notebooks that the sorted pages of mail go into are written.